Method for adjusting consistency

ABSTRACT

Disclosed herein is a met,hod for adjusting the consistency of concrete mix by adding an water-absorbing polymeric material or a thickening agent of carboxymethylcellulose to a fresh concrete mix.

This is a continuation of Ser. No. 08/264,931 filed Jun. 24, 1994, nowabandoned, which is a continuation of Ser. No. 07/935,103, filed Aug.27, 1992, now U.S. Pat. No. 5,332,434.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for adjusting the consistencyof a fresh concrete mix at the site of concrete placement, and moreparticularly to a method for adjusting the plasticity and fluidity of aconcrete mix which vary depending on the amount of water.

2. Description of the Prior Art

It is known well that the consistency of a concrete mix is one of themost important factors governing concrete placement. A stiff-consistencyconcrete mix having a low slump value involves difficulties inplacement. It requires much labor for compacting (which leads to lowefficiency) and is liable to honeycombing. On the other hand, asoft-consistency concrete mix having a high slump value has improvedworkability but is liable to bleeding and reduced strength anddurability (after hardening). A proper adjustment of consistency is veryimportant particularly for concrete structures such as concrete barrier,round aqueduct, and bridge retaining wall which are built continuouslyby slip form construction, and also for concrete structures such asU-shaped or L-shaped canals which need watertightness. In the case ofconcrete barrier, a concrete mix having a low slump value gives rise toweak concrete due to an excessive void content; by contrast, a concretemix having a high slump value easily deforms, with the upper surfacesinking and the body expanding.

Usually concrete mixing is not performed at the site but is performed ata concrete plant, and previously-mixed concrete is brought into the siteby agitator trucks. Under these circumstances, the adjustment ofconsistency is accomplished by adding admixtures such as cement, fly ashand mineral powder, to previously-mixed concrete brought into the site.The amount of the admixtures for this purpose is established accordingto the mix design, trial mix, and slump test. The conventional method,however, has a disadvantage of requiring the admixtures in largequantities. This necessitates a large scale facility and much labor tohandle the admixtures. Moreover, making adjustment intermittenty asagitator trucks arrive at the site poses a problem associated withmaintaining uniform quality, particularly in the case where a largequantity of concrete is to be placed. The present invention wascompleted to eliminate the above-mentioned disadvantages involved in theprior art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new method foradjusting the consistency of a concrete mix. To achieve the object ofthe invention, the present inventors paid their attention to thedevelopment of a new water absorbing polymer. It is known that naturalfiber and polymer (such as paper and cotton cloth) and porous materials(such as synthetic cellular products and pumice stone) absorb water.These materials, however, can only absorb and hold as much water astheir weight, or several tens times at the highest. Moreover, theyeasily release the absorbed water under external pressure. This resultsin concrete having insufficient strength and hence jeopardizes thesafety and durability of the structures.

A recently developed water absorbing polymeric material comprising oneof a copolymer of acrylic acid with vinyl alcohol, and a polymer ofsodium acrylate, is capable of absorbing tens to hundreds times as muchwater as its weight. Its absorbing capacity for city water is nearly1000 times its weight. In addition, it absorbs water rapidly and retainsthe absorbed water even when it receives external pressure. Theabsorbing capacity for city water decreases by one order of magnitude inthe presence of calcium ions and decreases by another one order ofmagnitude in the presence of external pressure by gravel and sand. Theamount of the water-absorbing polymer required for the adjustment ofconsistency is 2 kg per m³ of previously-mixed concrete, assuming thatabout 20 kg of water per m³ of concrete mix has to be absorbed for thereduction of a slump value, as an example, from 8 cm to 3 cm.

The water-absorbing polymeric material is in the form of spherical orgranular powder of micron size. Recently, it is also available in theform of short fiber or pellet for easy handling.

The gist of the present invention resides in a method for adjusting theconsistency of a concrete mix at the site by adding the above-mentionedwater-absorbing polymeric material to a fresh concrete mix. The methodis applicable to a high slump concrete mix prepared at a concrete plantand brought into the site by an agitator truck. The concrete mix isincorporated with the water-absorbing polymeric material during itsremixing and conveyance by a screw feeder. The resulting concrete mixhas its consistency adjusted so that it is suitable for slip formconstruction and the like.

Moreover, in order to achieve the above-mentioned object, the presentinventors paid their attention to a water-soluble thickening agentcalled CMC (carboxymethylcellulose), which finds use as an adhesive forfiber board and plywood and also as an ingredient for drilling mud. Asis commonly known, this water-soluble thickening agent has the followingfeatures.

(1) It readily dissolves in cold water as well as hot water to give aviscous solution.

(2) Its solution does not change in viscosity with time.

(3) Its solution readily emulsifies a liquid or disperses a solid.

(4) Its solution exhibits adhesive properties.

(5) It does not dissolve in oil, grease, and organic solvents.

(6) It is harmless to the human body.

(7) It is uniform and consistent in quality.

(8) It is in the form of powder or granule which is easy to handle.

Utilizing these features of thickening agent, the present inventorssucceeded in adjusting the consistency of a concrete mix at the site byadding CMC (as a thickening agent) to previously-mixed concrete beforehardening. The method is applicable to a high slump concrete mixprepared at a concrete plant and brought into the site by an agitatortruck. The concrete mix is incorporated with CMC (as a thickening agentin the form of powder or granule) during its remixing and conveyance bya screw feeder. The resulting concrete mix has its consistency adjustedso that it is suitable for slip form construction and the like.

As mentioned above, the method of the present invention consists ofincorporating a concrete mix with a water-absorbing polymeric materialhaving a high water-absorbing capacity, or CMC which readily dissolvesin water to form a viscous solution which exhibits adhesive properties,thereby adjusting the consistency of a concrete mix. The method of thepresent invention obviates the necessity of using a large amount ofconventional admixtures such as cement and fly ash, but makes itpossible to adjust the consistency rapidly and adequately by adding onlya small amount of water-absorbing polymeric material or thickeningagent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows relation between slump of concrete and amount of admixture(water absorbing agent).

FIG. 2 shows relation between slump of concrete and amount of admixture(thickening agent).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described in more detail with reference to thefollowing examples.

Example 1

Previously-mixed concrete having a slump value of 8 cm, 12 cm and 18 cmwere prepared at a concrete plant according to the mix proportion asshown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Mix Proportion                                                                Max-                                                                              Water/                                                                            Unit volume of                                                                        Quantity per unit volume (kg/m.sup.3)                         imum                                                                              cement                                                                            coarse           Coarese                                                                            Fine                                                                              Water                                       size                                                                              ratio                                                                             aggre-           aggre-                                                                             aggre-                                                                            reduc-                                                                            AE                                      (mm)                                                                              (%) gate    Water                                                                             Cement                                                                             gate gate                                                                              er  agent                                   __________________________________________________________________________    1* 20                                                                             50  0.68    175 350  1024 739 0.875                                                                             0.07                                    2* 20                                                                             50  0.68    181 362  1024 714 0.905                                                                             0.04                                    3* 20                                                                             50  0.68    186 372  1024 692 0.930                                                                             0.02                                    __________________________________________________________________________     Remarks:                                                                      1* indicates slump value of 8 cm.,                                            2* indicates slump value of 12 cm. and                                        3* indicates slump value of 18 cm.                                       

These previously-mixed concrete were brought into the site by anagitator truck and then remixed. During remixing, a water-absorbingpolymeric material ( "IM-5000" made by Sanyo Chemical Industries, Ltd.,or "Glass Power " made by Kurita Kogyo Co., Ltd.) was added. Aftermixing, the concrete mix was tested for slump and air content at certaintime intervals. The results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Change with Time in Consistency                                               Kind of                                                                            Name of                                                                            Amount of                                                           admix-                                                                             admix-                                                                             admixture                                                                              Slump(cm)   Air content(%)                                 ture ture (kg/m.sup.3)                                                                       (wt %)                                                                            0 min.                                                                            5 min.                                                                            15 min.                                                                           0 min.                                                                            5 min.                                                                            15 min.                                __________________________________________________________________________    Base conc. slump value 8 cm.                                                                     8.0     6.5 5.2     4.6                                    Water                                                                              IM-5000                                                                            2.0  0.087                                                                             3.0 3.0 2.5         3.7                                    absorb-   1.0  0.044                                                                             5.5 5.0 4.0         3.8                                    ing  Glass                                                                              2.0  0.087                                                                             1.0                                                        agent                                                                              Power                                                                              1.0  0.044                                                                             3.0 2.5 2.0         3.7                                    Base conc. slump value 12 cm.                                                                    12.0    10.5                                                                              5.7     5.3                                    Water                                                                              IM-5000                                                                            3.0  0.132                                                                             3.0 2.5 2.5         5.0                                    absorb-   2.0  0.088                                                                             4.5 4.5 4.0         5.3                                    ing  Glass                                                                              2.0  0.088                                                                             2.0 2.0 1.5         4.5                                    agent                                                                              Power                                                                              1.5  0.066                                                                             3.5 3.5 3.0         4.9                                    Base conc. slump value 18 cm.                                                                    18.0    15.0                                                                              6.3     5.9                                    ater IM-5000                                                                            4.0  0.176                                                                             3.0 3.0 2.5         5.8                                    absorb-   3.0  0.132                                                                             4.0 3.5 3.5         5.7                                    ing  Glass                                                                              2.0  0.088                                                                             3.0 3.0 3.0         5.5                                    agent                                                                              Power                                                                              1.5  0.066                                                                             5.0 4.5 4.0         5.5                                    __________________________________________________________________________

The concrete mix incorporated with the water-absorbing agent was found,after hardening, to have slightly increased in strength as compared withthe control, as shown in Table 3. The concrete mix having a slump valuelower than 3 cm can be used for slip form construction which does notneed the fixing of framework. The results appeared in Table 2 are shownin the graphical drawing of FIG 1.

                  TABLE 3                                                         ______________________________________                                        Compression Strength                                                                                            Compressive                                 kind of Name of    Amount of admixture                                                                          strength                                    admixture                                                                             admixture  (kg/m.sup.3)   (kg/m.sup.3)                                ______________________________________                                        Base conc, slump value 8 cm.                                                                            325                                                 Water-  IM-5000    2.0            349                                         absorbing                                                                     agent   Glass Power                                                                              2.0            348                                         ______________________________________                                    

Example 2.

Previously mixed concrete having a slump value of 8 cm, 12 cm and 18 cmwere prepared at a concrete plant in the same manner as in Example 1,according to the mix proportion as shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Mix Proportion                                                                Max-                                                                              Water/                                                                            Unit volume of                                                                        Quantity per unit volume (kg/m.sup.3)                         imum                                                                              cement                                                                            coarse           Coarese                                                                            Fine                                                                              Water                                       size                                                                              ratio                                                                             aggre-           aggre-                                                                             aggre-                                                                            reduc-                                                                            AE                                      (mm)                                                                              (%) gate    Water                                                                             Cement                                                                             gate gate                                                                              er  agent                                   __________________________________________________________________________    1* 20                                                                             50  0.68    175 350  1024 739 0.875                                                                             0.07                                    2* 20                                                                             50  0.68    181 362  1024 714 0.805                                                                             0.04                                    3* 20                                                                             50  0.68    186 372  1024 682 0.830                                                                             0.02                                    __________________________________________________________________________     Remarks:                                                                      1* indicates slump value of 8 cm,                                             2* indicates slump value of 12 cm and                                         3* indicates slump value of 18 cm.                                       

These previously-mixed concrete were brought into the site by anagitator truck and then remixed. During remixing, a thickening agent ofcarboxymethylcellulose ("Sesuka" made by Daiichi Kogyo Seiyaku K.K. or"Kacelose" made by 8Shikoku Kasei Kogyo K. K.) was added. After mixing,the concrete mix was tested for slump and air content at certain timeintervals. The results are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________    Change with Time in Consistency                                               Kind of                                                                            Name of                                                                            Amount of                                                           admix-                                                                             admix-                                                                             admixture                                                                              Slump (cm)  Air content(%)                                 ture ture (kg/cm.sup.3)                                                                      (wt %)                                                                            0 min.                                                                            5 min.                                                                            15 min.                                                                           0 min.                                                                            5 min.                                                                            15 min.                                __________________________________________________________________________    Base conc. slump value 8 cm.                                                                     8.0     6.5 5.2     4.6                                    Thick-                                                                             Sesuka                                                                             0.4  0.017                                                                             3.5     3.0 5.1     4.8                                    ening     0.2  0.008                                                                             5.0     4.0 5.1     6.0                                    agent                                                                              Kacelose                                                                           0.8  0.035                                                                             3.5     3.0 5.0     4.8                                              0.4  0.017                                                                             5.5     4.5 5.3     5.1                                    Base conc. slump value 12 cm.                                                                    12.0    10.5                                                                              5.7     5.3                                    Thick-                                                                             Sesuka                                                                             0.6  0.026                                                                             3.0     2.5         5.5                                    ening     0.4  0.018                                                                             4.5     4.0         5.3                                    agent                                                                              Kacelose                                                                           1.0  0.044                                                                             3.0     2.5         5.2                                              0.8  0.035                                                                             4.0     3.5         4.9                                    Base conc. slump value 18 cm.                                                                    18.0    15.0                                                                              6.3     5.9                                    Thick-                                                                             Sesuka                                                                             0.8  0.035                                                                             3.0     3.0         5.5                                    ening     0.6  0.026                                                                             3.0     2.5         6.0                                    agent                                                                              Kacelose                                                                           1.2  0.053                                                                             3.0     3.0         5.8                                              0.8  0.044                                                                             4.5     4.5         6.2                                    __________________________________________________________________________

The concrete mix incorporated with the thickening agent was found, afterhardening, to have slightly increased in strength as compared with thecontrol, as shown in Table 6. The concrete mix having a slump valuelower than 3 cm can be used for slip form construction which does notneed the fixing of framework. The results appeared in Table 5 are shownin graphical drawing FIG. 2.

Effect of the Invention

As mentioned above, Example 1 demonstrated the following effects whenthe consistency of previously-mixed concrete is adjusted byincorporation with a water-absorbing polymeric material having a veryhigh water absorbing capacity which rapidly absorbs water inpreviously-mixed concrete and firmly retains the absorbed water.

(1) The adjustment of consistency is possible with a very small amountof water absorbing polymeric material. A desired value of consistencycan be selected at any time measured by minute.

(2) The water-absorbing polymeric material, which is in the form ofpowder or granule, is easy to handle. It can be added to thepreviously-mixed concrete brought in to the site by an agitator truck.This makes it unnecessary to construct a separate concrete plant forslip form construction but permits the use of an existing concreteplant.

(3) The concrete mix with its consistency adjusted by the method of thepresent invention can be readily applied to slip form construction whichobviates the necessity of providing and removing forms.

(4) The water-absorbing polymeric material has no adverse effect on thequality of concrete after curing and hardening. Example 2 produced thesame effects as above, in which the consistency of previously-mixedconcrete was adjusted by adding a thickening agent comprisingcarboxymethylcellulose which readily dissolves in water to give aviscous solution which exhibits adhesive properties. (Refer to Table 6,Compressive Strength.)

                  TABLE 6                                                         ______________________________________                                        Compression Strength                                                                             Amount        Compressive                                  Kind of  Name of   of admixture  Strength                                     admixture                                                                              admixture (kg/m.sup.3)                                                                            (wt %)                                                                              (kg/m.sup.3)                               ______________________________________                                        Base conc. slump value 8 cm.                                                                           341                                                  Thickening                                                                             Sesuka    0.4       0.017 331                                        agent    Kacelose  0.8       0.035 347                                        ______________________________________                                    

What is claimed is:
 1. A method for adjusting the consistency ofpreviously-mixed concrete by adding water-absorbing polymeric materialscomprising one of a copolymer of acrylic acid with vinyl alcohol, and apolymer of sodium acrylate to the previously mixed concrete, the methodis characterized in that the previously-mixed concrete having a slumpvalue of 5-18 cm is added with one of the water-absorbing polymericmaterials selected from one of the copolymer of acrylic acid with vinylalcohol, and the polymer of sodium acrylate in a ratio of 1.0-4.0 kg(0.03-0.18 wt%) per m³ of said previously-mixed concrete to adjust theconsistency of said previously-mixed concrete to a slump value of lowerthan 3 cm before hardening.
 2. A method for adjusting the consistency ofpreviously-mixed concrete by adding a thickening agent comprisingcarboxymethylcellulose, the method is characterized in that thepreviously-mixed concrete having a slump value of 5-18 cm is added withthe carboxymethylcellulose ratio of 0.4-1.2 kg (0.01-0.06 wt%) per m³ ofsaid previously-mixed concrete to adjust the consistency of saidpreviously-mixed concrete to a slump value of lower than 3 cm beforehardening.